The proposed research entails the behavioral analysis of the variation in sound-localization ability among mammals. The primary goal of this research consists of the determination of the selective pressures involved in the evolution of hearing and sound localization. In the course of the study we also hope to identify a species lacking the ability to use the binaural intensity difference cue to localize sound and which would be more convenient for studying the neuroanatomy and electrophysiology underlying this peculiar lack of ability. Finally, a survey of the variation in the central auditory system among Artiodactyls and Perissodactyls will be continued. The short-range goals concern the behavioral assessment of hearing and sound localization ability (both free field and using headphones) in five species of mammals: weasels, badgers, goats, sheep, and pigs. Each species has been carefully selected based on ecological, phyletic, and anatomical factors known or suspected to influence the ability to localize sound. Through such a comparative analysis of mammalian sound localization, it is hoped to gain information concerning the factors influencing the evloution of hearing and sound-localization in man.